Due to the conductivity of the SM thermal bath, diffusion processes tend to wash out the primordial hypermagnetic fields permeating the early Universe.
These processes are particularly efficient at small scales, but reach the correlation length of the hypercharge gauge field at a temperature scale of around [1]}
\(T_{\rm diff} \sim \frac{1}{c_\lambda ^2} \frac{T}{\sigma _{\rm th}} H_{\rm end} \,,\) 
